Pneumatic tire

ABSTRACT

Provided is a pneumatic tire. A sipe includes, on each of a leading side edge and a trailing side edge, a chamfered portion and a non-chamfered region including no other chamfered portion. The maximum depth of the chamfered portion is shallower than the maximum depth of the sipe, and the sipe width is substantially constant. In a cross-sectional view, at least one chamfered portion includes a profile line that is convex inward in a tire radial direction with respect to a chamfer reference line connecting both ends of the chamfered portion; and a cross-sectional area of a chamfered region that is surrounded by the profile line, the sipe, and a tread contact surface of a tread portion is equal to or greater than a cross-sectional area of a reference region, the reference region being surrounded by the chamfer reference line, the sipe, and the tread contact surface.

TECHNICAL FIELD

The present technology relates to a pneumatic tire, and moreparticularly, to a pneumatic tire capable of improving steeringstability performance on a dry road surface and improving steeringstability performance on a wet road surface and includes a chamferedshape of a sipe.

BACKGROUND ART

Conventionally, in a tread pattern of a pneumatic tire, a plurality ofsipes are formed on ribs defined by a plurality of main grooves. Suchsipes are provided such that drainage properties are ensured andsteering stability performance on a wet road surface is achieved.However, when a large number of sipes are disposed in the tread portionfor improving the steering stability performance on the wet roadsurface, the rigidity of the rib is reduced, so there is a disadvantagethat steering stability performance on a dry road surface isdeteriorated.

Various proposals have been made on pneumatic tires in which sipes areformed in a tread pattern and chamfered (see, for example, JapanUnexamined Patent Publication No. 2013-537134). When forming a sipe andchamfering it, the edge effect may be lost depending on the shape ofchamfer, and improvement in steering stability performance on a dry roadsurface or steering stability performance on a wet road surface may beinsufficient depending on the chamfering size.

SUMMARY

The present technology provides a pneumatic tire capable of achievingboth improvement of steering stability performance on a dry road surfaceand improvement of steering stability performance on a wet road surfaceand includes a chamfer shape of a sipe.

A pneumatic tire of the present technology includes a plurality of maingrooves extending in a tire circumferential direction in a treadportion, and a sipe extending in a tire width direction in a rib definedby the plurality of main grooves. The sipe includes a leading side edgeand a trailing side edge, a chamfered portion shorter than a sipe lengthof the sipe is formed in each of the leading side edge and the trailingside edge, a non-chamfered region including no other chamfered portionis present in a part facing each chamfered portion of the sipe, amaximum depth y (mm) of the chamfered portion is shallower than amaximum depth x (mm) of the sipe, a sipe width of the sipe is constantin a range from an end positioned on a radial direction inside of thechamfered portion to a groove bottom of the sipe, at least one of thechamfered portions when viewed as a cross-section perpendicular to alongitudinal direction of the sipe includes a profile line that isconvex inward in a tire radial direction with respect to a chamferreference line connecting both ends of the chamfered portion, and across-sectional area a of a chamfered region surrounded by the profileline, the sipe, and a tread contact surface of the tread portion isequal to or larger than a cross-sectional area b of a reference regionsurrounded by the chamfer reference line, the sipe, and the treadcontact surface.

According to the present technology, in a pneumatic tire including asipe extending in the tire width direction on a rib defined by a maingroove, while a chamfered portion shorter than the sipe length of thesipe is formed in each of the leading side edge and the trailing sideedge of the sipe, there is a non-chamfered region including no otherchamfered portion in the part facing each chamfered portion in the sipe,thereby improving the drainage effect based on the chamfered portion andat the same time the non-chamfered region is capable of effectivelyremoving the water film by the edge effect. This thereby enablessteering stability on wet road surfaces to be significantly improved.Moreover, since the chamfered portion and the non-chamfered region aremixed in each of the leading side edge and the trailing side edge, thebeneficial effect of improving the wet performance as described abovemay be maximized at the time of braking and at the time of accelerating.Further, compared to the sipe chamfered in a conventional manner, sincethe area to be chamfered can be minimized, improvement in steeringstability performance on dry road surfaces is enabled. As a result,achieving both the improvement of steering stability performance on dryroad surfaces and the improvement of steering stability performance onwet road surfaces is enabled. Further, since at least one of thechamfered portions when viewed as a cross-section perpendicular to alongitudinal direction of the sipe includes a profile line that isconvex inward in a tire radial direction with respect to a chamferreference line connecting both ends of the chamfered portion, and sincea cross-sectional area a of a chamfered region surrounded by the profileline, the sipe, and a tread contact surface of the tread portion isequal to or larger than a cross-sectional area b of a reference regionsurrounded by the chamfer reference line, the sipe, and the treadcontact surface, an increase in the groove volume is enabled withoutreducing the contact area, thereby enabling the steering stabilityperformance on a wet road surface to be improved while maintaining thesteering stability performance on a dry road surface.

In the present technology, the cross-sectional area a of the chamferedregion is preferably in the range of from 110% to 210% of thecross-sectional area b of the reference region. More preferably, it isfrom 130% to 180%. This enables the steering stability performance onthe wet road surface to be improved without deteriorating the steeringstability performance on the dry road surface.

In the present technology, the volume Va of the chamfered region ispreferably in the range of from 110% to 210% of the volume Vb of thereference region. More preferably, it is from 110% to 140%. This enablesthe steering stability performance on the wet road surface to beimproved without deteriorating the steering stability performance on thedry road surface.

In the present technology, when a position at which the chamferreference line and the profile line of the chamfered portion arefarthest apart is set as an offset position, it is preferable that anoffset distance A, which is a distance from a width direction end of thesipe on a tire surface to the offset position, be in a range of from105% to 200% of a reference distance B, which is on a same straight lineas the offset distance A and which is also a distance from a widthdirection end of the sipe on a tire surface to the chamfer referenceline. More preferably, it is from 110% to 140%. This enables thesteering stability performance on the wet road surface to be improvedwithout deteriorating the steering stability performance on the dry roadsurface.

In the present technology, it is preferable that the maximum depth x(mm) of the sipe and the maximum depth y (mm) of the chamfered portionsatisfy the relationship of the following formula (1). This enables thesteering stability performance on the dry road surface and the steeringstability performance on the wet road surface to be improvedeffectively.x×0.1≤y≤x×0.3+1.0  (1)

In the present technology, when a distance from a width direction end ofthe sipe on a tire surface to an offset position, which is a position atwhich the chamfer reference line and the profile line of the chamferedportion are most distant from each other, is set as an offset distanceA, it is preferable that at least one side of the chamfered portions beopen to the main groove, and in the chamfered portion open to the maingroove, the offset distance A at a main groove side end be larger thanthe offset distance A at a rib center side end. This enables the groovevolume to be increased as it is positioned toward the main groove sidein the chamfered portion open to the main groove, such that the drainageproperty is effectively improved and the steering stability performanceon the wet road surface is improved.

In the present technology, it is preferable that in the chamferedportion open to the main groove, the offset distance A at the rib centerside end be 0.5 to 0.9 times the offset distance A at the main grooveside end. More preferably, it is 0.6 to 0.8 times. This enables thegroove volume to be increased as it is positioned toward the main grooveside in the chamfered portion open to the main groove, such that thedrainage property is effectively improved and the steering stabilityperformance on the wet road surface is improved.

In the present technology, it is preferable that at least one side ofthe chamfered portions be open to the main groove, and in the chamferedportion open to the main groove, a cross-sectional area a of thechamfered region at the main groove side end be larger than across-sectional area a of the chamfered region at the rib center sideend. This enables the groove volume to be increased as it is positionedtoward the main groove side in the chamfered portion open to the maingroove, such that the drainage property is effectively improved and thesteering stability performance on the wet road surface is improved.

In the present technology, it is preferable that in the chamferedportion open to the main groove, the cross-sectional area a of thechamfered region at the rib center side end be 0.5 to 0.9 times thecross-sectional area a of the chamfered region at the main groove sideend. More preferably, it is 0.6 to 0.8 times. This enables the groovevolume to be increased as it is positioned toward the main groove sidein the chamfered portion open to the main groove, such that the drainageproperty is effectively improved and the steering stability performanceon the wet road surface is improved.

In the present technology, a mounting direction of the pneumatic tirewith respect to a vehicle is designated, the pneumatic tire having atread pattern asymmetric with respect to two sides of a tire centerline, and when a distance from a width direction end of the sipe on atire surface to an offset position, which is a position at which thechamfer reference line and the profile line of the chamfered portion aremost distant from each other, is set as an offset distance A, it ispreferable that in the rib, the offset distance A of the chamferedportion located toward the vehicle inner side be larger than the offsetdistance A of the chamfered portion located toward the vehicle outerside. This enables the steering stability performance on the wet roadsurface to be improved effectively without deteriorating the steeringstability performance on the dry road surface.

In the present technology, it is preferable that the offset distance Aof the chamfered portion located toward the vehicle outer side be 0.5 to0.9 times the offset distance A of the chamfered portion located towardthe vehicle inner side. More preferably, it is 0.6 to 0.8 times. Thisenables the steering stability performance on the wet road surface to beimproved effectively without deteriorating the steering stabilityperformance on the dry road surface.

In the present technology, a mounting direction of the pneumatic tirewith respect to a vehicle is designated, the pneumatic tire having atread pattern asymmetric with respect to two sides of a tire centerline, and it is preferable that, in the rib, a cross-sectional area a ofthe chamfered region at the chamfered portion located toward the vehicleinner side be larger than a cross-sectional area a of the chamferedregion at the chamfered portion located toward the vehicle outer side.This enables the steering stability performance on the wet road surfaceto be improved effectively without deteriorating the steering stabilityperformance on the dry road surface.

In the present technology, it is preferable that the cross-sectionalarea a of the chamfered region at the chamfered portion located towardthe vehicle outer side be 0.5 to 0.9 times the cross-sectional area a ofthe chamfered region at the chamfered portion located toward the vehicleinner side. More preferably, it is 0.6 to 0.8 times. This enables thesteering stability performance on the wet road surface to be improvedeffectively without deteriorating the steering stability performance onthe dry road surface.

In the present technology, a mounting direction of the pneumatic tirewith respect to a vehicle is designated, the pneumatic tire having atread pattern asymmetric with respect to two sides of a tire centerline, and it is preferable that, in the rib, a volume Va of thechamfered region at the chamfered portion located toward the vehicleinner side be larger than a volume Va of the chamfered region at thechamfered portion located toward the vehicle outer side. This enablesthe steering stability performance on the wet road surface to beimproved effectively without deteriorating the steering stabilityperformance on the dry road surface.

In the present technology, it is preferable that a volume Va of thechamfered region at the chamfered portion located toward the vehicleouter side be 0.5 to 0.9 times a volume Va of the chamfered region atthe chamfered portion located toward the vehicle inner side. Morepreferably, it is 0.6 to 0.8 times. This enables the steering stabilityperformance on the wet road surface to be improved effectively withoutdeteriorating the steering stability performance on the dry roadsurface.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a meridian cross-sectional view illustrating a pneumatic tireaccording to an embodiment of the present technology.

FIG. 2 is a perspective view illustrating part of a tread portion of apneumatic tire according to the present technology.

FIG. 3 is a plan view illustrating part of a tread portion of apneumatic tire according to the present technology.

FIG. 4 is a plan view illustrating a sipe and a chamfered portionthereof formed in the tread portion of FIG. 3.

FIGS. 5A-5D illustrate a sipe and a chamfered portion thereof formed inthe tread portion of the pneumatic tire of FIG. 3, FIG. 5A is across-sectional view taken along a line X-X, FIG. 5B is an enlargedcross-sectional view of the chamfered portion of the sipe of FIG. 5A,FIG. 5C illustrates the chamfered region Ra, and FIG. 5D illustrates thechamfered region Rb.

FIG. 6 is a plan view illustrating a modified example of a sipe and achamfered portion thereof formed in a tread portion of a pneumatic tireaccording to the present technology.

FIG. 7 is a plan view illustrating another modified example of a sipeand a chamfered portion thereof formed in a tread portion of a pneumatictire according to the present technology.

FIGS. 8A and 8B illustrate another modified example of a sipe and achamfered portion thereof of a pneumatic tire according to the presenttechnology, and FIGS. 8A and 8B are plan views of the respectivemodifications.

FIG. 9 is a cross-sectional view taken along the line Y-Y of FIG. 3.

DETAILED DESCRIPTION

Configuration of embodiments of the present technology are described indetail below with reference to the accompanying drawings. In FIG. 1, CLis the tire equatorial plane.

As illustrated in FIG. 1, a pneumatic tire according to embodiments ofthe present technology includes an annular tread portion 1 extending inthe tire circumferential direction, a pair of sidewall portions 2, 2disposed on both sides of the tread portion 1, and a pair of beadportions 3, 3 disposed inward of the sidewall portions 2 in the tireradial direction.

A carcass layer 4 is mounted between the pair of bead portions 3, 3. Thecarcass layer 4 includes a plurality of reinforcing cords extending inthe tire radial direction and is folded back around bead cores 5disposed in each of the bead portions 3 from a tire inner side to a tireouter side. A bead filler 6 having a triangular cross-sectional shapeformed from rubber composition is disposed on the outer circumference ofthe bead core 5.

A plurality of belt layers 7 are embedded on an outer circumferentialside of the carcass layer 4 in the tread portion 1. The belt layers 7include a plurality of reinforcing cords that are inclined with respectto the tire circumferential direction with the reinforcing cords of thedifferent layers arranged in a criss-cross manner. In the belt layers 7,an inclination angle of the reinforcing cords with respect to the tirecircumferential direction ranges from, for example, 10° to 40°. Steelcords are preferably used as the reinforcing cords of the belt layers 7.To improve high-speed durability, at least one belt cover layer 8 formedby arranging reinforcing cords at an angle of, for example, not greaterthan 5° with respect to the tire circumferential direction, is disposedon an outer circumferential side of the belt layers 7. Nylon, aramid, orsimilar organic fiber cords are preferably used as the reinforcing cordsof the belt cover layer 8.

Also, a plurality of main grooves 9 extending in the tirecircumferential direction is formed in the tread portion 1. These maingrooves 9 define the tread portion 1 into a plurality of rows of ribs10.

Note that the tire internal structure described above represents atypical example for a pneumatic tire, and the pneumatic tire is notlimited thereto. FIGS. 2 to 4 illustrate a part of the tread portion 1,Tc indicates the tire circumferential direction, and Tw indicates thetire width direction. As illustrated in FIG. 2, the rib 10 includes aplurality of sipes 11 extending in the tire width direction, and a block101 defined by the sipes 11. The plurality of blocks 101 are arranged toline up in the tire circumferential direction. In addition, the sipe 11is an open sipe penetrating the rib 10 in the tire width direction, andboth ends of the sipe 11 communicate with the main grooves 9 located onboth sides of the rib 10. Furthermore, the sipe 11 may be a closed sipewhose opposite ends terminate in the rib 10, or may be a semi-closedsipe in which only one end of the sipe 11 terminates in the rib 10. Thesipe 11 is a narrow groove having a groove width of 1.5 mm or less.

As illustrated in FIG. 3, the sipe 11 has a curved shape as a whole, andis formed in the rib 10 at intervals in the tire circumferentialdirection. Further, the sipe 11 includes an edge 11A which is on theleading side with respect to the rotation direction R, and an edge 11Bwhich is on the trailing side with respect to the rotation direction R.A chamfered portion 12 is formed on each of the edge 11A on the leadingside and the edge 11B on the trailing side.

The chamfered portion 12 includes a chamfered portion 12A which is onthe leading side with respect to the rotation direction R and achamfered portion 12B which is on the trailing side with respect to therotation direction R. There is a non-chamfered region 13 including noother chamfered portion in the part facing the chamfered portion 12.Namely, there is a non-chamfered region 13B which is on the trailingside with respect to the rotational direction R at a part facing thechamfered portion 12A and a non-chamfered region 13A which is on theleading side with respect to the rotational direction R at a part facingthe chamfered portion 12B. In this manner, the chamfered portion 12 andthe non-chamfered region 13 including no other chamfered portion aredisposed adjacent to each other on each of the edge 11A on the leadingside and the edge 11B on the trailing side of the sipe 11.

As illustrated in FIG. 4, in the sipe 11 and the chamfered portions 12Aand 12B, the length in the tire width direction is set as the sipelength L, the chamfered lengths L_(A) and L_(B), respectively. Thesesipe length L and the chamfered lengths L_(A) and L_(B) are the lengthin the tire width direction from one end to the other end of each of thesipes 11 or the chamfered portions 12A and 12B. The chamfered lengthsL_(A) and L_(B) of the chamfered portions 12A and 12B are both formed tobe shorter than the sipe length L of the sipe 11.

FIG. 5A is a cross-sectional view perpendicular to the sipe 11, in whichthe tread portion 1 is cut out in the vertical direction. As illustratedin FIG. 5A, when the maximum depth of the sipe 11 is set as x (mm) andthe maximum depth of the chamfered portion 12 is set as y (mm), the sipe11 and the chamfered portion 12 are formed such that the maximum depth y(mm) becomes shallow than the maximum depth x (mm). The maximum depth xof the sipe 11 is preferably from 3 mm to 8 mm. The sipe width W of thesipe 11 is substantially constant in a range from the end 121 located onthe inner side in the tire radial direction of the chamfered portion 12to the groove bottom of the sipe 11. The sipe width W is determined suchthat the width is the substantially measured width of the sipe 11, forexample, in a case that a ridge exists on the groove wall of the sipe11, by not including the height of the ridge in the sipe width, or in acase that the sipe width of the sipe 11 gradually narrows toward thegroove bottom, by not including the narrowed portion in the sipe width.

FIG. 5B is an enlarged view of the chamfered portion 12 illustrated inFIG. 5A. As illustrated in FIG. 5B, in a cross-sectional viewperpendicular to the longitudinal direction of the sipe 11, a linesegment connecting the ends 121 and 122 of the chamfered portion 12 isdefined as a chamfer reference line RL. At least one of the chamferedportions 12A and 12B includes a profile line OL that is convex inward inthe tire radial direction from the chamfer reference line RL. The regionsurrounded by the profile line OL, the sipe 11 and the tread contactsurface of the tread portion 1 is defined as a chamfered region Ra (seeFIG. 5C); and the region surrounded by the chamfer reference line RL,the sipe 11, and the tread contact surface is set as a reference regionRb (see FIG. 5D). Namely, the fan-shaped region surrounded by the twodotted lines and the profile line OL illustrated in FIG. 5B is thechamfered region Ra as illustrated in FIG. 5C, and the triangular areaenclosed between the two dotted lines and the chamfer reference line RLillustrated in FIG. 5B is the reference region Rb as illustrated in FIG.5D. At this time, a cross-sectional area a of the chamfered region Ra isequal to a cross-sectional area b of the reference region Rb or largerthan the cross-sectional area b of the reference region Rb (see FIGS.5C-5D). In particular, the cross-sectional area a of the chamferedregion Ra is preferably larger than the cross-sectional area b of thereference region Rb.

In the chamfered portions 12A and 12B, in the embodiment illustrated inFIGS. 5A and 5B, an example is illustrated in which the entire profileline OL has a shape convex inward in the tire radial direction from thechamfer reference line RL. However, it is also possible to locallyprovide a shape convex inward in the tire radial direction from thechamfer reference line RL at a part of the profile line OL.

In the above-described pneumatic tire, by providing a chamfered portion12 shorter than the sipe length L of the sipe 11 in each of a leadingside edge 11A and a trailing side edge 11B of the sipe 11, and sincethere is a non-chamfered region 13 including no other chamfered portionin the part facing each chamfered portion 12 in the sipe 11, thedrainage effect is improved based on the chamfered portion 12, and atthe same time the non-chamfered region 13 is capable of effectivelyremoving the water film by the edge effect. This thereby enablessteering stability on wet road surfaces to be significantly improved.Moreover, since the chamfered portion 12 and the non-chamfered region 13including no chamfered portion are mixed in each of the leading sideedge 11A and the trailing side edge 11B, the beneficial effect ofimproving the wet performance as described above may be maximized at thetime of braking and at the time of accelerating. Further, since at leastone of the chamfered portions 12 when viewed as a cross-sectionperpendicular to a longitudinal direction of the sipe 11 includes aprofile line OL that is convex inward in a tire radial direction from achamfer reference line RL connecting both ends of the chamfered portion,and since a cross-sectional area a of a chamfered region Ra surroundedby the profile line OL, the sipe 11, and a tread contact surface of thetread portion 1 is equal to or larger than a cross-sectional area b of areference region Rb surrounded by the chamfer reference line RL, thesipe 11, and the tread contact surface, an increase in the groove volumeis enabled without reducing the contact area, thereby enabling thesteering stability performance on a wet road surface to be improvedwhile maintaining the steering stability performance on a dry roadsurface.

In the above-described pneumatic tire, it is preferable that the maximumdepth x (mm) and the maximum depth y (mm) satisfy the relationship ofthe following formula (1). Providing the sipe 11 and the chamferedportion 12 so as to satisfy the relationship of the following formula(1) enables the area to be chamfered to be minimized compared with thesipe provided with the conventional chamfering, thereby enabling thesteering stabilizing performance on the dry road surface to be improved.As a result, achieving both the improvement of steering stabilityperformance on dry road surfaces and the improvement of steeringstability performance on wet road surfaces is enabled. Here, if y<x×0.1,the drainage effect based on the chamfered portion 12 becomesinsufficient, and conversely, if y>x×0.3+1.0, the rigidity of the rib 10deteriorates, lowering the steering stability performance. It isparticularly preferable to satisfy the relation y≤x×0.3+0.5.x×0.1≤y≤x×0.3+1.0  (1)

In the above-described pneumatic tire, the cross-sectional area a of thechamfered region Ra is preferably in the range of from 110% to 210%, andmore preferably from 130% to 180%, of the cross-sectional area b of thereference region Rb. Appropriately setting the cross-sectional area a ofthe chamfered region Ra with respect to the cross-sectional area b ofthe reference region Rb in this manner enables the steering stabilityperformance on the wet road surface to be improved without deterioratingthe steering stability performance on the dry road surface.

Further, the volume Va of the chamfered region Ra is preferably in therange of 110% to 210%, and more preferably from 110% to 140%, of thevolume Vb of the reference region Rb. Appropriately setting the volumeVa of the chamfered region Ra with respect to the volume Vb of thereference region Rb in this manner enables the steering stabilityperformance on the wet road surface to be improved without deterioratingthe steering stability performance on the dry road surface.

As illustrated in FIG. 5B, the offset position P is the position wherethe chamfer reference line RL and the profile line OL of the chamferedportion 12 are most distant from each other. A distance from a widthdirection end of the sipe 11 on the tire surface to the offset positionP is set as the offset distance A, and a distance, on a same straightline as the offset distance A, from the width direction end of the sipe11 on the tire surface to the chamfer reference line RL is set as thereference distance B. In this case, the offset distance A of thechamfered portion 12 is preferably in the range of from 105% to 200%,and more preferably from 110% to 140%, of the reference distance B.Appropriately setting the offset distance A of the chamfered portion 12with respect to the reference distance B in this manner enables thesteering stability performance on the wet road surface to be improvedwithout deteriorating the steering stability performance on the dry roadsurface.

At least one of the chamfered portions 12A and 12B positioned on theleading side and trailing side of the sipe 11 is open to the main groove9. In the chamfered portion 12 open to the main groove 9, the offsetdistance A at the main groove 9 side end is larger than the offsetdistance A at the rib 10 center side end. In particular, the offsetdistance A at the rib 10 center side end is preferably configured to be0.5 to 0.9 times, and more preferably 0.6 to 0.8 times, the offsetdistance A at the main groove 9 side end. Providing the chamferedportion 12 in this manner enables the groove volume to be increased asthe chamfered portion 12 is positioned toward the main groove 9 side inthe chamfered portion 12 open to the main groove 9, such that thedrainage property is effectively improved and the steering stabilityperformance on the wet road surface is improved.

In addition, in the chamfered portion 12 open to the main groove 9, thecross-sectional area a of the chamfered region Ra at the main groove 9side end is larger than the cross-sectional area a of the chamferedregion Ra at the rib 10 center side end. In particular, thecross-sectional area a of the chamfered region Ra at the rib 10 centerside end is preferably configured to be 0.5 to 0.9 times, and morepreferably 0.6 to 0.8 times, the cross-sectional area a of the chamferedregion Ra at the main groove 9 side end. Providing the chamfered portion12 in this manner enables the groove volume to be increased as thechamfered portion 12 is positioned toward the main groove 9 side in thechamfered portion 12 open to the main groove 9, such that the drainageproperty is effectively improved and the steering stability performanceon the wet road surface is improved.

FIG. 6 illustrates another modification of the sipe 11 and the chamferedportion 12 thereof formed in the tread portion 1 of the pneumatic tireaccording to the present technology. In FIG. 6, a mounting direction ofthe pneumatic tire with respect to a vehicle is designated, thepneumatic tire has a tread pattern asymmetric with respect to two sidesof a tire center line, and IN denotes the vehicle inner side and OUTdenotes the vehicle outer side.

In the above-described pneumatic tire, and in the same rib 10, theoffset distance A of the chamfered portion 12 positioned on the vehicleinner side is larger than the offset distance A of the chamfered portion12 positioned on the vehicle outer side. In particular, the offsetdistance A of the chamfered region Ra positioned toward the vehicleouter side is preferably configured to be 0.5 to 0.9 times, and morepreferably 0.6 to 0.8 times, the offset distance A of the chamferedregion Ra positioned toward the vehicle inner side. Providing thechamfered portion 12 in this manner enables the steering stabilityperformance to be improved effectively on the wet road surface withoutdeteriorating the steering stability performance on the dry roadsurface.

In the above-described pneumatic tire, and in the same rib 10, thecross-sectional area a of the chamfered region Ra at the chamferedportion 12 positioned on the vehicle inner side is larger than thecross-sectional area a of the chamfered region Ra at the chamferedportion 12 positioned on the vehicle outer side. In particular, thecross-sectional area a of the chamfered region Ra positioned toward thevehicle outer side is preferably configured to be 0.5 to 0.9 times, andmore preferably 0.6 to 0.8 times, the cross-sectional area a of thechamfered region Ra positioned toward the vehicle inner side. Providingthe chamfered portion 12 in this manner enables the steering stabilityperformance to be improved effectively on the wet road surface withoutdeteriorating the steering stability performance on the dry roadsurface.

Furthermore, in the above-described pneumatic tire, and in the same rib10, the volume Va of the chamfered region Ra at the chamfered portion 12positioned on the vehicle inner side is larger than the volume Va of thechamfered region Ra at the chamfered portion 12 positioned on thevehicle outer side. In particular, the volume Va of the chamfered regionRa positioned toward the vehicle outer side is preferably configured tobe 0.5 to 0.9 times, and more preferably 0.6 to 0.8 times, the volume Vaof the chamfered region Ra positioned toward the vehicle inner side.Providing the chamfered portion 12 in this manner enables the steeringstability performance to be improved effectively on the wet road surfacewithout deteriorating the steering stability performance on the dry roadsurface.

FIG. 7 illustrates another modification of the sipe 11 and the chamferedportion 12 thereof formed in the tread portion 1 of the pneumatic tireaccording to the present technology. The sipe 11 illustrated in FIG. 7is formed to have an inclination angle θ with respect to the tirecircumferential direction. The inclination angle θ refers to an angleformed between a virtual line (a dotted line illustrated in FIG. 7)connecting both ends of the sipe 11 and a side surface of the block 101.There is an inclination angle on the acute angle side and an inclinationangle on the obtuse angle side, and the inclination angle θ on the acuteangle side is illustrated in FIG. 7. The inclination angle θ is targetedfor the inclination angle of the sipe 11 with an intermediate pitch inthe rib 10. In this case, the inclination angle θ on the acute angleside is preferably 40° to 80°, and more preferably 50° to 70°. Byinclining the sipe 11 with respect to the circumferential direction ofthe tire in this manner, the pattern rigidity can be improved, and thesteering stability performance on the dry road surface can be furtherimproved. Here, when the inclination angle θ is smaller than 40°, theuneven wear resistance deteriorates, and when it exceeds 80°, thepattern rigidity cannot be sufficiently improved.

In the present technology, the side having the inclination angle θ onthe acute angle side of the sipe 11 is defined as the acute angle side,and the side having the inclination angle θ on the obtuse angle side ofthe sipe 11 is defined as the obtuse angle side. The chamfered portions12A and 12B formed on the edges 11A and 11B of the sipe 11 are formed onthe acute angle side of the sipe 11. Chamfering the acute angle side ofthe sipe 11 as described above enables the uneven wear resistanceperformance to be further improved. Alternatively, the chamferedportions 12A and 12B may be formed on the obtuse angle side of the sipe11. Forming the chamfered portion 12 on the obtuse angle side of thesipe 11 as described above enables the edge effect to be increased andthe steering stability performance on the wet road surface to be furtherimproved.

In the present technology, having the entire shape of the sipe 11 curvedas described above enables the steering stability performance to beimproved on the wet road surface. Further, a part of the sipe 11 may becurved or bent in a plan view. Forming the sipe 11 in this mannerincreases the total amount of the edges 11A, 11B in each sipe 11,enabling the steering stability performance on the wet road surface tobe improved.

As illustrated in FIG. 7, one chamfered portion 12 is disposed on eachof the edge 11A on the leading side and the edge 11B on the trailingside of the sipe 11. Having the chamfered portions 12 disposed in thismanner enables the uneven wear resistance performance to be improved.Here, forming the chamfered portion 12 in two or more places on the edge11A on the leading side and the edge 11B on the trailing side of thesipe 11 increases the number of nodes and tends to deteriorate theuneven wear resistance performance.

Here, the maximum value of the width of the chamfered portion 12measured along the direction orthogonal to the sipe 11 is defined as awidth W1. In this case, the maximum width W1 of the chamfered portion 12is preferably 0.8 to 5.0 times, and more preferably 1.2 to 3.0 times,the sipe width W of the sipe 11. Setting the maximum width W1 of thechamfered portion 12 with respect to the sipe width W at an appropriatevalue in this manner enables both the steering stability performance onthe dry road surface and the steering stability performance on the wetroad surface to be improved. Here, when the maximum width W1 of thechamfered portion 12 is smaller than 0.8 times the sipe width W of thesipe 11, the improvement of the steering stability performance on thewet road surface is made insufficient, and if it is larger than 5.0times, the improvement of the steering stability performance on the dryroad surface is made insufficient.

Further, the outer edge portion in the longitudinal direction of thechamfered portion 12 is formed to be parallel to the extending directionof the sipe 11. Having the chamfered portion 12 extended in parallelwith the sipe 11 in this manner enables the uneven wear resistanceperformance to be improved, and at the same time enables both thesteering stability performance on the dry road surface and the steeringstability performance on the wet road surface to be improved.

As illustrated in FIG. 7, ends of the chamfered portions 12A, 12Bpositioned closer to the main groove 9 do not communicate with the maingrooves 9 located on both sides of the rib 10 but terminate in the rib10. Forming the chamfered portion 12 in this manner enables the steeringstability performance on the dry road surface to be further improved.Alternatively, the ends of the chamfered portions 12A, 12B positionedcloser to the main groove 9 may communicate with the main groove 9.Forming the chamfered portion 12 in this manner enables the steeringstability performance on the wet road surface to be further improved.

As illustrated in FIG. 8A, the chamfered portion 12A and the chamferedportion 12B are formed so that part of both chamfered portions 12A, 12Boverlap each other at the central portion of the sipe 11. Here, thelength in the tire width direction of the overlap portion, which is aportion where the chamfered portion 12A and the chamfered portion 12Boverlap, is set as an overlap length L1. On the other hand, asillustrated in FIG. 8B, in a case that part of both chamfered portions12A and chamfered portion 12B do not overlap and are spaced apart fromeach other at a certain interval, the ratio of the overlap length L1 tothe sipe length L is expressed as a negative value. The overlap lengthL1 of the overlap portion is preferably from −30% to 30%, and morepreferably from −15% to 15%, of the sipe length L. Appropriatelyconfiguring the overlap length L1 in the chamfered portion 12 withrespect to the sipe length L in this manner enables both the steeringstability performance on the dry road surface and the steering stabilityperformance on a wet road surface to be both achieved. Here, if theoverlap length L1 is larger than 30%, the improvement in the steeringstability performance on the dry road surface becomes insufficient, andif it is smaller than −30%, the improvement in the steering stabilityperformance on the wet road surface becomes insufficient.

As illustrated in FIG. 9, the sipe 11 includes a bottom raised portion14 in a part of the longitudinal direction thereof. The bottom raisingportion 14 includes a bottom raised portion 14A positioned at thecentral portion of the sipe 11, and a raised bottom portion 14Bpositioned at both ends of the sipe 11. Providing the bottom raisedportion 14 in the sipe 11 in this manner enables improvement in steeringstability performance on a dry road surface and improvement in steeringstability performance on a wet road surface to be both achieved. Thebottom raised portion 14 of the sipe 11 may be formed at an end portionand/or a non-end portion of the sipe 11.

The height of the bottom raised portion 14 in the tire radial directionformed in the sipe 11 is defined as a height H₁₄. The maximum value ofthe height from the groove bottom of the sipe 11 to the upper surface ofthe bottom raised portion 14A in the bottom raised portion 14A formedbesides the end of the sipe 11 is set as the height H_(14A). This heightH_(14A) is preferably 0.2 to 0.5 times, and more preferably 0.3 to 0.4times, the maximum depth x of the sipe 11. Setting the height H_(14A) ofthe bottom raised portion 14A disposed at a position other than the endof the sipe 11 at an appropriate height in this manner enables therigidity of the block 101 to be improved and the drainage effect to bemaintained, thereby improving steering stability performance on a wetroad surface. Here, if the height H_(14A) is smaller than 0.2 times themaximum depth x of the sipe 11, the rigidity of the block 101 cannot besufficiently improved, and if it is larger than 0.5 times, steeringstability performance on a wet road surface cannot be sufficientlyimproved.

In the bottom raised portion 14B formed at both ends of the sipe 11, themaximum value of the height from the groove bottom of the sipe 11 to theupper surface of the bottom raised portion 14B is set as the heightH_(14B). This height H_(14B) is preferably 0.6 to 0.9 times, and morepreferably 0.7 to 0.8 times, the maximum depth x of the sipe 11. Settingthe height H_(14B) of the bottom raised portion 14B formed at the end ofthe sipe 11 at an appropriate height in this manner enables the rigidityof the block 101 to be improved, enabling the steering stabilityperformance on the dry road surface to be improved. Here, if the heightH_(14B) is smaller than 0.6 times the maximum depth x of the sipe 11,the rigidity of the block 101 cannot be sufficiently improved, and if itis larger than 0.9 times, steering stability performance on a wet roadsurface cannot be sufficiently improved.

Further, the length in the tire width direction at the bottom raisedportion 14 of the sipe 11 is set as the bottom raised length L₁₄. Theraised lengths L_(14A) and L_(14B) of the raised bottom portions 14A and14B are preferably 0.3 to 0.7 times, and more preferably 0.4 to 0.6times, the sipe length L. Appropriately setting the raised lengthsL_(14A) and L_(14B) of the bottom raised portions 14A and 14B in thismanner enables the improvement of the steering stability performance onthe dry road surface and the improvement of the steering stabilityperformance on the wet road surface to be both achieved.

EXAMPLES

In a pneumatic tire including a plurality of main grooves extending inthe tire circumferential direction in a tread portion and includingsipes extending in the tire width direction on a rib defined by the maingrooves with a tire size of 245/40 R19, the following items were set asshown in Table 1, and the tires of Conventional Example 1, theComparative Examples 1 and 2, and the Examples 1 to 5 were manufacturedaccordingly: the chamfer arrangement (both sides or one side); therelationship between the sipe length L and the chamfer lengths L_(A),L_(B); whether a chamfer in the part facing the chamfered portion ispresent; the sipe width; the sipe maximum depth x (mm); the chamferedportion maximum depth y (mm); the ratio of offset distance A toreference distance B (A/B×100%); the ratio of chamfered regioncross-section area a to reference region cross-section area b(a/b×100%); and the ratio of chamfered region volume Va to referenceregion volume Vb (Va/Vb×100%).

In all of these test tires, the sipes formed in the ribs are open sipeswhose both ends communicate with the main groove. In addition, the sipewidth in Table 1 denotes whether the sipe width is constant within therange from the end located in the tire radial direction inside thechamfered portion to the groove bottom of the sipe.

These test tires were tested by a test driver for a sensory evaluationof steering stability performance on dry road surfaces and steeringstability performance on wet road surfaces, with the result indicated inTable 1.

Sensory evaluations on driving stability performance on dry roadsurfaces and steering stability performance on wet road surfaces wereconducted by assembling each test tire to a rim size 19×8.5 J wheel andmounting it on a vehicle with air pressure of 260 kPa. Evaluationresults are expressed as index values, with the results of ConventionalExample 1 being assigned an index value of 100. Larger index valuesindicate superior driving stability performance on a dry road surfaceand superior driving steering stability performance on a wet roadsurface.

TABLE 1 Conventional Comparative Comparative Example 1 Example 1 Example2 Chamfer arrangement (both Both sides One side Both sides sides or oneside) Relationship between sipe L = L_(A), L_(B) L = L_(A) L > L_(A),L_(B) length L and chamfer length L_(A), L_(B) Whether chamfer in partYes No No facing chamfered portion is present Sipe width Constant Withchange Constant Sipe maximum depth x 6 mm 6 mm 6 mm (mm) Chamferedportion 3 mm 3 mm 3 mm maximum depth y (mm) Ratio of offset distance A100 100 100 to reference distance B (A/B × 100%) Ratio of chamferedregion 100 100 100 cross-section area a to reference region cross-section area b (a/b × 100%) Ratio of chamfered region 100 100 100 volumeVa to reference region volume Vb (Va/Vb × 100%) Dry road surfacesteering 100  90 103 stability performance Wet road surface steering 100105 103 stability performance Example 1 Example 2 Example 3 Example 4Example 5 Chamfer arrangement (both Both Both Both Both Both sides orone side) sides sides sides sides sides Relationship between sipe L >L_(A), L > L_(A), L > L_(A), L > L_(A), L > L_(A), length L and chamferL_(B) L_(B) L_(B) L_(B) L_(B) length L_(A), L_(B) Whether chamfer inpart No No No No No facing chamfered portion is present Sipe widthConstant Constant Constant Constant Constant Sipe maximum depth x 6 mm 6mm 6 mm 6 mm 6 mm (mm) Chamfered portion 3 mm 3 mm 3 mm 3 mm 2 mmmaximum depth y (mm) Ratio of offset distance A 103 107 110 115 115 toreference distance B (A/B × 100%) Ratio of chamfered region 105 109 112115 115 cross-section area a to reference region cross- section area b(a/b × 100%) Ratio of chamfered region 105 109 109 112 112 volume Va toreference region volume Vb (Va/Vb × 100%) Dry road surface steering 103103 103 103 105 stability performance Wet road surface steering 105 107108 110 110 stability performance

As can be seen from Table 1, by devising the shape of the chamferedportion formed in the sipe, steering stability performance on a dry roadsurface and steering stability performance on a wet road surface weresimultaneously improved in the tires of Examples 1 to 5 in comparisonwith Conventional Example 1.

On the other hand, in Comparative Example 1, since the chamfered portionwas disposed only on one side and the sipe width was not constant,although the wet road surface steering stability performance wasimproved, the effect of improving the dry road surface steeringstability performance was not sufficiently obtained. In ComparativeExample 2, since the chamfered portion does not include a profile linethat is convex inward in the tire radial direction from the chamferreference line in a cross-sectional view perpendicular to thelongitudinal direction of the sipe, improvement effect for the dry roadsurface steering stability performance did not reach that of Example 1.

Next, similarly to Conventional Example 1, Comparative Examples 1 and 2,and Examples 1 to 5, in a pneumatic tire including a plurality of maingrooves extending in the tire circumferential direction in a treadportion and including sipes extending in the tire width direction on arib defined by the main grooves with a tire size of 245/40 R19, thetires of Conventional Example 2, Comparative Examples 3 and 4, andExamples 6 to 9 were manufactured, in which offset distance A toreference distance B ratio (A/B×100%), and chamfered regioncross-section area a to reference region cross-section area b ratio(a/b×100%) are different between the rib center side and the main grooveside. In the Conventional Example 2, Comparative Examples 3 and 4, andExamples 6 to 9, the chamfer arrangement (both sides or one side), therelationship between the sipe length L and the chamfer lengths L_(A),L_(B), whether a chamfer in the part facing the chamfered portion ispresent, the sipe width; the sipe maximum depth x (mm), the chamferedportion maximum depth y (mm), the ratio of offset distance A toreference distance B (A/B×100%), and the ratio of chamfered regioncross-section area a to reference region cross-section area b(a/b×100%), were set as illustrated in Table 2.

These test tires were tested by a test driver for a sensory evaluationof steering stability performance on a dry road surface and steeringstability performance on a wet road surface, with the results alsoindicated in Table 2.

TABLE 2 Conventional Comparative Comparative Example 2 Example 3 Example4 Chamfer arrangement (both sides or Both sides One side Both sides oneside) Relationship between sipe length L L = L_(A), L_(B) L = L_(A) L >L_(A), L_(B) and chamfer lengths L_(A), L_(B) Whether chamfer in partfacing Yes No No chamfered portion is present Sipe width Constant Withchange Constant Sipe maximum depth x (mm) 6 mm 6 mm 6 mm Chamferedportion maximum depth 3 mm 3 mm 3 mm y (mm) Ratio of offset Rib centerside 100 100 100 distance A to Main groove side 100 100 100 referencedistance B (A/B × 100%) Ratio of Rib center side 100 100 100 chamferedregion Main groove side 100 100 100 cross-section area a to referenceregion cross- section area b (a/b × 100%) Dry road surface steeringstability 100  90 103 performance Wet road surface steering stability100 105 103 performance Example 6 Example 7 Example 8 Example 9 Chamferarrangement (both sides or Both Both Both Both one side) sides sidessides sides Relationship between sipe length L L > L_(A), L > L_(A), L >L_(A), L > L_(A), and chamfer lengths L_(A), L_(B) L_(B) L_(B) L_(B)L_(B) Whether chamfer in part facing No No No No chamfered portion ispresent Sipe width Constant Constant Constant Constant Sipe maximumdepth x (mm) 6 mm 6 mm 6 mm 6 mm Chamfered portion maximum depth 2 mm 2mm 2 mm 2 mm y (mm) Ratio of offset Rib center side 115 115 115 115distance A to Main groove side 120 130 130 130 reference distance B (A/B× 100%) Ratio of Rib center side 115 115 115 115 chamfered region Maingroove side 115 115 120 130 cross-section area a to reference regioncross- section area b (a/b × 100%) Dry road surface steering stability105 105 105 105 performance Wet road surface steering stability 111 113114 116 performance

As can be seen from Table 2, by devising the shape of the chamferedportion formed in the sipe, steering stability performance on a dry roadsurface and steering stability performance on a wet road surface weresimultaneously improved in the tires of Examples 6 to 9 in comparisonwith Conventional Example 2.

On the other hand, in Comparative Example 3, since the chamfered portionwas disposed only on one side and the sipe width was not constant,although the wet road surface steering stability performance wasimproved, the effect of improving the dry road surface steeringstability performance was not obtained sufficiently. In ComparativeExample 4, since the chamfered portion does not include a profile linethat is convex inward in the tire radial direction from the chamferreference line in a cross-sectional view perpendicular to thelongitudinal direction of the sipe, improvement effect for the dry roadsurface steering stability performance did not reach that of Example 6.

Further, similarly to Conventional Example 1, Comparative Examples 1 and2, and Examples 1 to 5, in a pneumatic tire including a plurality ofmain grooves extending in the tire circumferential direction in a treadportion and including sipes extending in the tire width direction on arib defined by the main grooves with a tire size of 245/40 R19, thetires of Conventional Example 3, Comparative Examples 5 and 6, andExamples 10 to 16 were manufactured, in which the ratio of offsetdistance A to reference distance B (A/B×100%), ratio of chamfered regioncross-section area a to reference region cross-section area b(a/b×100%), and the ratio of chamfered region volume Va to referenceregion volume Vb (Va/Vb×100%) are different between the vehicle innerside and the vehicle outer side. In the Conventional Example 3,Comparative Examples 5 and 6, and Examples 10 to 16, the chamferingarrangement (both sides or one side), relationship between the sipelength L and the lengths of the chamfer lengths L_(A), L_(B), whether achamfer in the part facing the chamfered portion is present, the sipewidth, the sipe maximum depth x (mm), the chamfered portion maximumdepth y (mm), the ratio of offset distance A to reference distance B(A/B×100%), the ratio of chamfered region cross-section area a toreference region cross-section area b (a/b×100%), the ratio of chamferedregion volume Va to reference region volume Vb (Va/Vb×100%), and whetherthe bottom raised portion is present, were set as shown in Table 3.

These test tires were tested by a test driver for a sensory evaluationof steering stability performance on dry road surfaces and steeringstability performance on wet road surfaces, with the results alsoindicated in Table 3.

TABLE 3 Conventional Comparative Comparative Example 3 Example 5 Example6 Chamfer arrangement (both sides Both sides One side Both sides or oneside) Relationship between sipe length L = L_(A), L_(B) L = L_(A) L >L_(A), L_(B) L and chamfer length L_(A), L_(B) Whether chamfer in partfacing Yes No No chamfered portion is present Sipe width Constant Withchange Constant Sipe maximum depth x (mm) 6 mm 6 mm 6 mm Chamferedportion maximum 3 mm 3 mm 3 mm depth y (mm) Ratio of offset distanceVehicle 100 100 100 A to reference distance B inner (A/B × 100%) sideVehicle 100 100 100 outer side Ratio of chamfered Vehicle 100 100 100region cross-section area inner a to reference region side cross-sectionarea b Vehicle 100 100 100 (a/b × 100%) outer side Ratio of chamferedVehicle 100 100 100 region volume Va to inner reference region volumeside Vb (Va/Vb × 100%) Vehicle 100 100 100 outer side Whether bottomraised portion is No No No present Dry road surface steering stability100  90 103 performance Wet road surface steering stability 100 105 103performance Example Example Example Example Example Example Example 1011 12 13 14 15 16 Chamfer arrangement Both Both Both Both Both Both Both(both sides or one side) sides sides sides sides sides sides sidesRelationship between L > L_(A), L > L_(A), L > L_(A), L > L_(A), L >L_(A), L > L_(A), L > L_(A), sipe length L and L_(B) L_(B) L_(B) L_(B)L_(B) L_(B) L_(B) chamfer length L_(A), L_(B) Whether chamfer in No NoNo No No No No part facing chamfered portion is present Sipe widthConstant Constant Constant Constant Constant Constant Constant Sipemaximum depth x 6 mm 6 mm 6 mm 6 mm 6 mm 6 mm 6 mm (mm) Chamferedportion 2 mm 2 mm 2 mm 2 mm 2 mm 2 mm 2 mm maximum depth y (mm) Ratio ofoffset Vehicle 117 130 130 130 130 130 130 distance A to inner referenceside distance B Vehicle 115 115 115 115 115 115 115 (A/B × 100%) outerside Ratio of Vehicle 115 115 117 130 130 130 130 chamfered inner regioncross- side section area a Vehicle 115 115 115 115 115 115 115 toreference outer region cross- side section area b (a/b × 100%) Ratio ofVehicle 112 112 112 112 117 130 130 chamfered inner region volume sideVa to reference Vehicle 112 112 112 112 112 112 112 region volume outerVb (Va/Vb × side 100%) Whether bottom raised No No No No No No Yesportion is present Dry road surface 105 105 105 105 105 105 107 steeringstability performance Wet road surface 111 113 114 116 117 118 118steering stability performance

As can be seen from Table 3, by devising the shape of the chamferedportion formed in the sipe, steering stability performance on a dry roadsurface and steering stability performance on a wet road surface weresimultaneously improved in the tires of Examples 10 to 16 in comparisonwith Conventional Example 3.

On the other hand, in Comparative Example 5, since the chamfered portionwas disposed only on one side and the sipe width was not constant,although the wet road surface steering stability performance wasimproved, the effect of improving the dry road surface steeringstability performance was not obtained sufficiently. In ComparativeExample 6, since the chamfered portion does not include a profile linethat is convex inward in the tire radial direction from the chamferreference line in a cross-sectional view perpendicular to thelongitudinal direction of the sipe, improvement effect for the dry roadsurface steering stability performance did not reach that of Example 10.

The invention claimed is:
 1. A pneumatic tire, comprising: a pluralityof main grooves extending in a tire circumferential direction in a treadportion; a sipe extending in a tire width direction in a rib defined bythe plurality of main grooves; the sipe comprising a leading side edgeand a trailing side edge; a chamfered portion shorter than a sipe lengthof the sipe being formed in each of the leading side edge and thetrailing side edge; a non-chamfered region comprising no other chamferedportion being present in a part facing each chamfered portion of thesipe; a maximum depth y (mm) of the chamfered portion being shallowerthan a maximum depth x (mm) of the sipe; a sipe width of the sipe beingconstant in a range from an end positioned on an inner side of thechamfered portion in a tire radial direction to a groove bottom of thesipe; at least one of the chamfered portions, when viewed as across-section perpendicular to a longitudinal direction of the sipe,comprising a profile line that is concave in the tire radial directionwith respect to a chamfer reference line connecting both ends of thechamfered portion; and a cross-sectional area a of a chamfered regionsurrounded by the profile line, the sipe, and a tread contact surface ofthe tread portion being equal to or larger than a cross-sectional area bof a reference region surrounded by the chamfer reference line, thesipe, and the tread contact surface; wherein each of the chamferedportions have a sipe edge extending along a length direction of the sipewhere the chamfered portions meet the sipe and an opposite edge oppositethe sipe edge, where a tire width direction component of a length of thesipe edge in the tire width direction is shorter than a tire widthdirection component of a length of the opposite edge in the tire widthdirection.
 2. The pneumatic tire according to claim 1, wherein thecross-sectional area a of the chamfered region is in a range of from110% to 210% of the cross-sectional area b of the reference region. 3.The pneumatic tire according to claim 1, wherein a volume Va of thechamfered region is in a range of from 110% to 210% of a volume Vb ofthe reference region.
 4. The pneumatic tire according to claim 1,wherein, when a position at which the chamfer reference line and theprofile line of the chamfered portion are farthest apart is set as anoffset position, an offset distance A, which is a distance from a widthdirection end of the sipe on a tire surface to the offset position, isin a range of from 105% to 200% of a reference distance B, which is on asame straight line as the offset distance A and which is also a distancefrom a width direction end of the sipe on the tire surface to thechamfer reference line.
 5. The pneumatic tire according to claim 1,wherein the maximum depth x (mm) of the sipe and the maximum depth y(mm) of the chamfered portion satisfy a relationship of a followingformula (1):x×0.1≤y≤x×0.3+1.0  (1).
 6. The pneumatic tire according to claim 1,wherein, when a distance from a width direction end of the sipe on atire surface to an offset position which is a position at which thechamfer reference line and the profile line of the chamfered portion aremost distant from each other, is set as an offset distance A, at leastone side of the chamfered portions is open to the main groove, and inthe chamfered portion open to the main groove, the offset distance A ata main groove side end is larger than the offset distance A at a ribcenter side end.
 7. The pneumatic tire according to claim 6, wherein, inthe chamfered portion open to the main groove, the offset distance A atthe rib center side end is 0.5 to 0.9 times the offset distance A at themain groove side end.
 8. The pneumatic tire according to claim 1,wherein, at least one side of the chamfered portions is open to the maingroove, and in the chamfered portion open to the main groove, across-sectional area a of the chamfered region at a main groove side endis larger than a cross-sectional area a of the chamfered region at a ribcenter side end.
 9. The pneumatic tire according to claim 8, wherein, inthe chamfered portion open to the main groove, the cross-sectional areaa of the chamfered region at the rib center side end is 0.5 to 0.9 timesthe cross-sectional area a of the chamfered region at the main grooveside end.
 10. The pneumatic tire according to claim 1, wherein, amounting direction of the pneumatic tire with respect to a vehicle isdesignated, the pneumatic tire having a tread pattern asymmetric withrespect to two sides of a tire center line, and when a distance from awidth direction end of the sipe on a tire surface to an offset position,which is a position at which the chamfer reference line and the profileline of the chamfered portion are most distant from each other, is setas an offset distance A, in the rib, the offset distance A of thechamfered portion located toward a vehicle inner side is larger than theoffset distance A of the chamfered portion located toward a vehicleouter side.
 11. The pneumatic tire according to claim 10, wherein, theoffset distance A of the chamfered portion located toward the vehicleouter side is 0.5 to 0.9 times the offset distance A of the chamferedportion located toward the vehicle inner side.
 12. The pneumatic tireaccording to claim 1, wherein, a mounting direction of the pneumatictire with respect to a vehicle is designated, the pneumatic tire havinga tread pattern asymmetric with respect to two sides of a tire centerline, and, in the rib, a cross-sectional area a of the chamfered regionat the chamfered portion located toward a vehicle inner side is largerthan a cross-sectional area a of the chamfered region at the chamferedportion located toward a vehicle outer side.
 13. The pneumatic tireaccording to claim 12, wherein, the cross-sectional area a of thechamfered region at the chamfered portion located toward the vehicleouter side is 0.5 to 0.9 times the cross-sectional area a of thechamfered region at the chamfered portion located toward the vehicleinner side.
 14. The pneumatic tire according to claim 1, wherein, amounting direction of the pneumatic tire with respect to a vehicle isdesignated, the pneumatic tire having a tread pattern asymmetric withrespect to two sides of a tire center line, and, in the rib, a volume Vaof the chamfered region at the chamfered portion located toward avehicle inner side is larger than a volume Va of the chamfered region atthe chamfered portion located toward a vehicle outer side.
 15. Thepneumatic tire according to claim 14, wherein, the volume Va of thechamfered region at the chamfered portion located toward the vehicleouter side is 0.5 to 0.9 times the volume Va of the chamfered region atthe chamfered portion located toward the vehicle inner side.